JP2583148B2 - Hydraulic control circuit of hydraulic excavator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a flow distribution at the time of simultaneous operation of a plurality of hydraulic actuators in a load sensing hydraulic control circuit of a hydraulic excavator. During the simultaneous operation of the boom and turning, such as loading work on a dump truck, correct the pressure of the flow rate supplied to each hydraulic actuator without changing the control pattern while being affected by other load pressures, and The present invention relates to a hydraulic control circuit of a hydraulic excavator that enables easy control and improves workability and saves energy.

[Conventional technology]

As shown in FIG. 2, a hydraulic excavator for excavating and loading earth and sand includes a traveling hydraulic motor 1 for a lower traveling body a, a hydraulic motor 2 for rotating an upper rotating body b, and a front part of the upper rotating body b. A boom 3, an arm 4, a bucket 5, and a hydraulic cylinder 6, 7, 8 for operating the work machine c are provided.

The hydraulic excavator performs a series of continuous operations such as excavation, lifting rotation, earth removal, and lifting rotation as the excavation work. In particular, lifting rotation is performed as shown in FIG. 3B, the arm 4 is in a dumping state, and as shown in FIG. 7B, the dumping operation is performed on the bed of the dump truck d stopped at a position near 45 °, 90 ° or 180 ° as shown in FIG. The swing circuit pressure is affected by the arm circuit and the boom circuit during simultaneous operation of the swing and the boom, and the swing and the arm. When the boom and the arm circuit are at a low pressure, the swing is also at a low pressure and the swing is not smoothly performed. In some cases, since the turning angle differs depending on the stop position of the dump truck d, the relationship between the turning angle and the boom angle changes.
Each time, by controlling the spool opening of the flow control valve of these hydraulic actuators, the supply flow rate to each circuit is controlled to adjust both movements, but this operation is very difficult. It was accompanied by fatigue.

[Problems to be solved by the invention]

In view of the above, the present invention has been made in consideration of the above-described problems, and in order to secure a required flow rate without a mutual influence of circuit pressures of these hydraulic actuators during simultaneous operation of turning and a boom, an arm, etc. The hydraulic excavator is designed to improve the work efficiency by changing the flow distribution by setting in advance and adapting the simultaneous operation by ensuring the control of the load sensing pressure control and the pressure compensation valve. It is an object to provide a hydraulic control circuit.

[Means for solving the problem]

In order to achieve the above object, a hydraulic control circuit of a hydraulic excavator according to the present invention comprises: (1) driven by two variable displacement hydraulic pumps and discharge pressure oil from each of the variable displacement hydraulic pumps. Boom, arm and swing hydraulic actuators, a flow control valve with pressure compensation for controlling each hydraulic actuator, and a differential pressure between the discharge pressure of each of the variable displacement hydraulic pumps and the maximum load pressure of each of the hydraulic actuators A hydraulic control circuit of a hydraulic excavator having a load sensing system for controlling a discharge flow rate of each of said variable displacement hydraulic pumps, wherein discharge hydraulic oils of said two hydraulic pumps 10 and 13 are combined or divided. , And a swing load sensing pressure switching valve 40 for turning on and off the load sensing pressure of the swing actuator, and a standard mode according to the work content. A work mode changeover switch 54 for selecting one of the work modes of the turning priority mode and the boom priority mode, and a signal selected from the work mode changeover switch 54, which is stored in advance corresponding to the signal. A controller 23 that outputs a command signal for switching the turning load sensing pressure switching valve 40 to an ON position or an OFF position while switching the merging / diverting switching valve 47 to a merging or branching position based on the stored data. It is configured.

(2) In the above configuration, the work mode selected by the work mode changeover switch 54 is a merge / divide flow changeover valve.
47 is the merging position, and swivel load sensing switching valve
A standard mode in which the ON / OFF position is set to 40, a turning priority mode in which the merging / diversion switching valve 47 is set to the diversion position, and the turning load sensing switching valve 40 is set to the OFF (in) position;
The boom priority mode is such that the diversion switching valve 47 is in the diversion position and the turning load sensing switching valve 40 is in the ON (off) position.

(Operation)

According to the above configuration, the work mode is selected according to the work content of the hydraulic excavator. (1) When the standard mode is selected, the command signal from the controller 23 is not transmitted to the pilot valve 50, Is in the position shown in FIG. Therefore, the pilot pressure acting on the operating portion of the merge / divide flow switching valve 47 is drained from the pilot line 48 to the tank 18.

As a result, the merging / shunting switching valve 47 is turned off and FIG.
At the merging position shown in the figure. At the same time, the command signal from the controller 23 is transmitted to the pilot valve 52,
52 is switched and the pilot pressure from the pilot pump 19 passes through the same valve 52 to act on the operating section of the swing load sensing switching valve 40 from the pilot line 41, and the valve 40 is turned on by operating to switch off. Position.

For this reason, the load pressure for driving the swing motor 1 is shut off by the swing load sensing switching valve 40, so that the load pressure of the actuator 6 of the boom is detected by the shuttle valve 38. This load pressure acts on the operation section of the load sensing valve 44a through the pilot line 29a, and acts on the operation section of the load sensing valve 44b through the pilot line 29b.

As a result, the discharge pressure P1 of the hydraulic pump 10 acts on one operation section of the load sensing valve 44a from the pipe 43a, and the load pressure LP1 of the actuator 6 of the boom guided from the pilot pipe 29a and the spring force are the same. Acting on the other operating part of the valve 44a, it is controlled to decrease the swash plate angle of the hydraulic pump 10 when P1> LP1, and to increase the swash plate angle of the hydraulic pump 10 when LP1 <P1. Controlled. Also, the discharge pressure P2 of the hydraulic pump 13
4b, the load pressure L of the actuator 6 of the boom guided from the pilot line 29b.
P2 and the spring force act on the other operating part of the valve 44b, and P2> L
When P2, the swash plate angle of the hydraulic pump 13 is controlled to decrease, and when LP2 <P2, the swash plate angle of the hydraulic pump 13 is controlled to increase.

That is, at the time of simultaneous operation of the boom and the swing in the standard mode, the swash plate angles of the hydraulic pumps 10 and 13 corresponding to the load pressure of the actuator 6 of the boom are controlled, and the required flow rate is supplied to each of the boom and swing actuators 6 and 1. Is done.

(2) When turning priority mode is selected, the controller
The command signal from 23 is transmitted to the pilot valve 50,
Is switched, the pilot pressure from the pilot pump 19 passes through the same valve 50 and merges from the pilot line 48,
Operates on 47 operation units. Therefore, the merging / shunting switching valve 47
Is turned ON to switch to the branch position. At the same time, the pilot pressure from the pilot pump 19 also acts on the operation section of the load sensing press-in / off switching valve 53, and the valve 53
Is switched to the position a. At this time, the command signal from the controller 23 is not transmitted to the pilot valve 52, and the pilot pressure acting on the operation unit of the valve 52 is transmitted from the pipe 41 to the tank 18
Drained. Therefore, the valve 52 is turned off and switched to the "on" position shown in FIG. As a result, the load pressure for driving the swing motor 1 passes through the swing load sensing switching valve 40 and the shuttle valve 34, and the pilot line 35
Through the pilot line 29b through the position b of the load sensing press-in / off switching valve 53, and the load sensing valve 44b
Acts on the operation unit.

Then, the discharge pressure P2 of the hydraulic pump 13 acts on one operation unit of the load sensing valve 44b from the pipeline 43b,
The load pressure LP2 and the spring force of the turning actuator 1 guided from the pilot line 29b act on the other operating portion of the valve 44b.

Thus, when P2> LP2, the swash plate angle of the hydraulic pump 13 is controlled to decrease, and when LP2 <P2, the swash plate angle of the hydraulic pump 13 is controlled to increase.

Therefore, when the turning priority mode is selected, the hydraulic pump 13 can independently supply the required flow rate to the turning actuator 1.

In this case, the actuator 6 of the boom is controlled by the differential pressure between the pump pressure P1 and the load pressure LP1 in the same manner as in the standard mode, and a required flow rate is supplied from the hydraulic pump 10.

That is, when the boom and the swing are simultaneously operated in the swing priority mode, the swash plate angle of the hydraulic pump 10 corresponding to the load pressure of the actuator 6 of the boom is controlled, and the hydraulic pump 13 corresponding to the load pressure of the swing actuator 1 is controlled. Is controlled. The required flow rate is supplied from each hydraulic pump 10, 13 to each of the boom and swing actuators 6, 1 independently.

(3) When the boom priority mode is selected, the command signal from the controller 23 is transmitted to the pilot valve 50,
50 is switched, the pilot pressure from the pilot pump 19 passes through the valve 50 and merges from the pilot line 48, acts on the operating portion of the branch flow switching valve 47, and the valve 47 is switched on by operating ON.
It becomes a branch position.

At the same time, the pilot pressure from the pilot pump 19 also acts on the operating section of the load sensing press-in / off switching valve 53, and switches the valve 53 to the position a. At this time, a command signal from the controller 23 is transmitted to the pilot valve 52, the valve 52 is turned ON and switched, and the pilot pressure from the pilot pump 19 is passed through the valve 52 and from the pilot line 41 to the turning load sensing. Acts on the operating part of the switching valve 40. Therefore, the valve 40 is turned ON to switch to the "OFF" position.

Therefore, the load pressure for driving the swing motor 1 is shut off by the swing load sensing switching valve 40.

Then, the load pressure of the actuator 6 of the boom passes through the pilot pipe 29a and acts on the operation section of the load sensing valve 44a, while the load pressure of the swing actuator 1 does not act on the operation section of the load sensing valve 44b.

As a result, the discharge pressure P1 of the hydraulic pump 10 acts on one operation portion of the load sensing valve 44a from the pipe 43a, and the load pressure LP1 and the spring force of the boom actuator 6 guided from the pilot pipe 29a are reduced. Acts on the other operating part of the valve 44a.

Therefore, when the differential pressure between the discharge pressure P1 of the hydraulic pump 10 and the load pressure LP1 of the boom actuator is P1> LP1, the swash plate angle of the hydraulic pump 10 is controlled to decrease, and LP1 <P
When 1, the swash plate angle of the hydraulic pump 10 is controlled to increase.

When the load pressure from the turning actuator 1 does not act on the load sensing valve 44b, the pressure is controlled by the discharge pressure P2 of the hydraulic pump 13. When the discharge pressure P2 becomes larger than the spring force, the swash plate angle is reduced. Is done.

When the boom priority mode is selected, the necessary flow rate is preferentially supplied to the actuator 1 of the boom.

When the actuator 7 of the arm is driven, the load pressure of the arm is supplied from the shuttle valve 34 via the pilot line 35 to the position b of the switching valve 53 and the pilot line 29b.
From the load sensing valve 44b.

Accordingly, when P2> LP2, the swash plate angle of the hydraulic pump 13 is controlled to decrease, and when LP2 <P2, the swash plate angle of the hydraulic pump 13 is controlled to increase. 7 can be supplied with the required flow rate.

That is, by selecting the boom priority mode,
Even when the turning angle is small (about 45 °), the operation of raising the boom can be sufficiently performed.

By selecting the above three operation modes according to the contents of the operation, simultaneous operability such as boom and turning can be improved.

〔Example〕

 An embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a hydraulic control circuit of a hydraulic excavator, in particular, a boom operating hydraulic cylinder 6 (hereinafter simply referred to as a boom cylinder) and an arm operating hydraulic cylinder 7 according to the present invention.
This embodiment shows a preferred embodiment of a hydraulic control circuit for three hydraulic actuators of an arm cylinder (hereinafter simply referred to as an arm cylinder) and a turning drive hydraulic motor 1 (hereinafter simply referred to as a turning motor). The boom cylinder 6 is connected to a discharge circuit 11 of one of the variable displacement hydraulic pumps 10, and the boom cylinder 6 is connected to the discharge circuit 11.
A flow control valve 12 with pressure compensation for controlling the flow rate and the flow direction is interposed between the discharge circuits 11, and a branch circuit is provided in the discharge circuit 14 of the other variable displacement hydraulic pump 13.
The swing cylinder 1 is connected to the arm cylinder 7 via the other branch circuit 14a, and the branch circuits 14a and 14b are connected to the flow control valves 15 and 16 with pressure compensation, respectively.
Is interposed. As described above, the boom cylinder 6, the arm cylinder 7, and the swing motor 1 are connected to the two hydraulic pumps 10, 1
3 and connected to a tank 18 via a return circuit 17. Each of the flow control valves 12, 15, 16 is of a pilot operation type, and is connected to both ends of each valve from a main line 20 of a pilot pump 19 via pilot lines 21a to 21f, respectively.

The operating levers 22a, 22b,
The operation from 22b and 22c is performed by the signal line 24a from the controller 23.
24f, and is controlled by pilot valves 25a to 25f, which are electromagnetic proportional control valves that are opened and closed by 24f.
26 is a return line for pilot hydraulic pressure. A hydraulic proportional control valve may be used instead of the pilot valves 25a to 25f formed of the electromagnetic proportional control valve.

Further, the pressure compensation control valves 12, 15, 16 detect the discharge pressures of the hydraulic pumps 10, 13 with respect to the required flow rates of the respective hydraulic actuators 6, 7, 1 and compensate the pressure compensation valves 27a, 27.
The hydraulic pumps b and 27c are provided, and are connected to the load sensing regulators 28a and 28b of the hydraulic pumps 10 and 13 via pilot pipelines 29a and 29b.

Next, as a load sensing circuit, a swirling flow control valve
The maximum load between the pilot line 33 for detecting the maximum load pressure of the swing motor 1 from the 15 outlet ports 32 and the pilot line 31 for detecting the maximum load pressure of the arm cylinder 7 from the outlet port 30 of the arm flow control valve 16 The maximum load pressure side pressure between the pilot line 35 that detects the pressure side pressure with the shuttle valve 34 and the pilot line 37 that detects the maximum load pressure of the boom cylinder 6 from the outlet port 36 of the boom flow control valve 12 is determined. After being detected by the shuttle valve 38, the hydraulic pump 10 is controlled by the pilot line 29a via the pilot line 29a.
Is connected to the load sensing regulator 28a of the other hydraulic pump 13 by a pilot line 29b. The load sensing circuit is provided with a switching valve 40 for turning load sensing press-in / off.

The switching valve 40 is controlled to be switched by an electromagnetic pilot valve 52 controlled by a signal circuit 51 of the control 23 via a pilot line 41.

Load sensing regulators 28a, 28b were connected by pilot lines 29a, 29b between pump discharge lines 11, 14 and servo pistons 42a, 42b for controlling the swash plate tilting amounts of hydraulic pumps 10, 13, respectively. It has load sensing valves 44a, 44b of a pilot operation type, the pilot lines 29a, 43a are provided at both ends of one load sensing valve 44a, and the pilot lines 29b, 44b are provided at both ends of the other load sensing valve 44b. 43b are connected respectively.

When the sum of the maximum load pressure guided by the pilot lines 29a and 29b and the spring force of the springs 45a and 45b becomes larger than the discharge pressure of the hydraulic pumps 10 and 13 guided by the pilot lines 43a and 43b, the load is reduced. When the sensing valves 44a and 44b are switched from the position (A) to the position (B), the pressure oil of the servo pistons 42a and 42b returns to the tank 18, increases the swash plate angle of the hydraulic pumps 10 and 13, and reduces the discharge flow rate. When the pressure increases and the sum of the load pressure and the spring force becomes smaller than the discharge pressure of the pump, the load sensing valves 44a and 44b are switched from the position (B) to the position (A), and the pilot lines 43a and 43b are switched. From the servo pistons 42a and 42b,
And the discharge flow rate is reduced.

That is, the discharge pressure P1 of the hydraulic pump 10 acts on one of the operation units of the load sensing valve 44a from the pipe 43a, and the load LP1 and the spring force guided from the pilot pipe 29a operate the other operation of the valve 44a. Act on the part.

Thus, when P1> LP1, the swash plate angle of the hydraulic pump 10 is controlled to decrease, and when LP1 <P1, the swash plate angle of the hydraulic pump 10 is controlled to increase. Also, the discharge pressure P2 of the hydraulic pump 13
While acting on one operating section of 4b, the load pressure LP2 and spring force led from the pilot line 29b act on the other operating section of the valve 44b.

Thus, when P2> LP2, the swash plate angle of the hydraulic pump 13 is controlled to decrease, and when LP2 <P2, the swash plate angle of the hydraulic pump 13 is controlled to increase.

By using the above-mentioned load sensing system and the flow control valve with pressure compensation 12,15,16, the hydraulic pump
Each of the pressure compensating valves 27a, 27b, 27c is controlled by the maximum load pressure of each of the hydraulic actuators 6, 7, 1 while saving energy by suppressing the required flow rate of the discharge pressure oils 10 and 13 to a desired level. As a result, the required flow rates with pressure compensation are supplied to the hydraulic actuators 6, 7, 1.

The discharge pipes 11 and 14 of the two variable displacement hydraulic pumps 10 and 13 are connected to the respective discharge pipes 11 and 14 by a communication pipe 46, and the discharge hydraulic oil of the two hydraulic pumps 10 and 13 is connected to the communication pipe 46. And a diverter valve 47 are provided.

The switching valve 47 is controlled to be switched by the pilot oil pressure in the pilot line 48 by the operation of the electromagnetic pilot valve 50 commanded from the controller 23 via the signal circuit 49.

A load sensing press-in / off switching valve 53 controlled in conjunction with the merging / diverting switching valve 47 is provided in the load sensing circuit.

The hydraulic control circuit of the hydraulic excavator composed of the load sensing system configured in this way includes excavation of earth and sand during lifting and turning, boom such as loading on a dump truck, and work distribution by simultaneous operation of arm and turning. The work modes in the table below are set in advance so that the matching can be changed. These work modes are selected by turning on / off the work mode changeover switch 54 by using the merging / shunting changeover valve 47 and the turning load sensing pressure changeover valve 40. Done by

(I) Standard mode When the 90 ° turning operation and the boom raising operation are performed simultaneously, work must be performed to secure approximately the same required flow rate that does not give priority to either the turning operation or the boom operation. The mode switch 54 is switched to the standard mode.

Thus, the command signal from the controller 23 is not transmitted to the pilot valve 50, and the valve 50 is at the position shown in FIG.

Therefore, the pilot pressure acting on the operating portion of the merge / divide flow switching valve 47 is drained from the pilot line 48 to the tank 18.

As a result, the merging / shunting switching valve 47 is turned off and FIG.
At the merging position shown in the figure.

At the same time, the command signal from the controller 23 is not transmitted to the pilot valve 52, and the pilot valve 52 is switched, and the pilot pressure from the pilot pump 19 passes through the valve 52 and from the pilot line 41 to the turning load sensing switching valve 40. And the valve 40 is turned ON to switch to the "OFF" position.

For this reason, the load pressure for driving the swing motor 1 is shut off by the swing load sensing switching valve 40, so that the load pressure of the boom cylinder 6 is detected by the shuttle valve 38. This load pressure passes through the pilot line 29a and passes through the load sensing valve 4
Acts on the operating section of 4a and also acts on the operating section of the load sensing valve 44b through the pilot line 29b.

Thus, the discharge pressure P1 of the hydraulic pump 10 acts on one operation portion of the load sensing valve 44a from the pipe 43a, and the load pressure LP1 of the boom cylinder 6 guided from the pilot pipe 29a and the spring force are the same. Acts on the other operating part of the valve 44a.

Therefore, when P1> LP1, the swash plate angle of the hydraulic pump 10 is controlled to decrease, and when LP1 <P1, the swash plate angle of the hydraulic pump 10 is controlled to increase.

In addition, the discharge pressure P2 of the hydraulic pump 13 acts on one operation unit of the load sensing valve 44b from the pipe 43b, and the load pressure LP2 of the boom cylinder 6 guided from the pilot pipe 29b and the spring force are the same. Acts on the other operation unit of 44b, and is controlled to decrease the swash plate angle of the hydraulic pump 13 when P2> LP2, and to increase the swash plate angle of the hydraulic pump 13 when LP2 <P2. Is done.

(II) Swing priority mode When the 180 ° turning operation and the boom raising operation are performed simultaneously, the mode is switched to the turning priority mode when the load pressure of the turning motor 1 is large and a large amount of flow is required. As a result, the command signal from the controller 23 is
The valve 50 is switched, and the pilot pressure from the pilot pump 19 passes through the valve 50 and joins from the pilot line 48 to act on the operating portion of the diverting valve 47.

For this reason, the merging / diverting switching valve 47 is turned on by being turned on to switch to the branching position.

At the same time, the pilot pressure from the pilot pump 19 also acts on the operating section of the load sensing press-in / off switching valve 53, and switches the valve 53 to the position a. At this time, the command signal from the control 23 is not transmitted to the pilot valve 52, and the pilot pressure acting on the operating portion of the
Drain from 41 to tank 18. Therefore, the valve 52
The operation is switched off to switch to the "on" position shown in FIG.

As a result, the load pressure for driving the swing motor 1 passes through the swing load sensing switching valve 40, through the shuttle valve 34, from the pilot line 35, through the a position of the load sensing press-in / off switching valve 53, and through the pilot line From 29b, it acts on the operation unit of the load sensing valve 44b.

The discharge pressure P2 of the hydraulic pump 13 acts on one operation section of the load sensing valve 44b from the pipe 43b, and the load pressure LP2 and the spring force of the swing motor 1 guided from the pilot pipe 29b are the same as those of the valve 44b. Acts on the other operating part.

Therefore, when P2> LP2, the swash plate angle of the hydraulic pump 13 is controlled to decrease, and when LP <P2, the hydraulic pump 13 is controlled.
Is controlled to increase the swash plate angle.

Therefore, when the swing priority mode is selected, the hydraulic pump 13 can independently supply the required flow rate to the swing motor 1.

In this case, the boom cylinder 6 is controlled by the differential pressure between the pump pressure P1 and the load pressure LP1 in the same manner as in the standard mode, and a required flow rate is supplied from the hydraulic pump 10.

(III) Boom priority mode When performing 45 ° turning operation and boom raising operation simultaneously, switch to the boom priority mode when the turning angle is relatively small and a large amount of flow is required for the boom raising operation. .

As a result, the command signal from the controller 23 is transmitted to the pilot valve 50, the valve 50 is switched, and the pilot pressure from the pilot pump 19 passes through the valve 50 and merges from the pilot line 48. Acts on the operation unit, and the same valve
47 is turned ON to switch to the shunt position.

At the same time, the pilot pressure from the pilot pump 19 also acts on the operating section of the load sensing press-in / off switching valve 53, and switches the valve 53 to the position a. At this time, a command signal from the controller 23 is transmitted to the pilot valve 52, the valve 52 is turned ON and switched, and the pilot pressure from the pilot pump 19 is passed through the valve 52 and from the pilot line 41 to the turning load sensing. Acts on the operating part of the switching valve 40. Therefore, the valve 40 is turned ON to switch to the "OFF" position.

Therefore, the load pressure for driving the swing motor 1 is shut off by the swing load sensing switching valve 40.

The load pressure of the boom cylinder 6 is
Through 29a, it acts on the operation part of the load sensing valve 44a.
Does not act on the operation part of 44b.

Thus, the discharge pressure P1 of the hydraulic pump 10 acts on one operation portion of the load sensing valve 44a from the pipe 43a, and the load pressure LP1 of the boom cylinder 6 guided from the pilot pipe 29a and the spring force are the same. Acts on the other operating part of the valve 44a.

For this reason, when the pressure difference between the discharge pressure P1 of the hydraulic pump 10 and the load pressure LP1 of the boom cylinder is P1> LP1, the hydraulic pump 10
Is controlled to decrease the swash plate angle, and when LP1 <P1, the swash plate angle of the hydraulic pump 10 is controlled to increase.

When the load pressure from the swing motor 1 does not act on the load sensing valve 44b, the pressure is controlled by the discharge pressure P2 of the hydraulic pump 13, and when the discharge pressure P2 becomes larger than the spring force, the swash plate angle is controlled to decrease. You.

Therefore, when the boom priority mode is selected, the required flow rate is supplied to the boom cylinder 6.

When the arm cylinder 7 is driven, the load pressure of the arm is transmitted from the shuttle valve 34 via the pilot line 35 to the operation portion of the load sensing valve 44b from the pilot line 29b through the a position of the switching valve 53 via the pilot valve 35. Works.

Accordingly, when P2> LP2, control is performed to decrease the inclination angle of the hydraulic pump 13, and when LP2 <P2, control is performed so as to increase the swash plate angle of the hydraulic pump 13. The required flow rate can be supplied.

That is, by selecting the boom priority mode,
Even when the turning angle is small (45 °), the operation of raising the boom can be sufficiently performed.

By selecting three working modes in this way,
Simultaneous operability such as boom and turning is improved according to the work content.

A monitor 55 displays each work mode setting on the monitor 55.

〔The invention's effect〕

As described above, according to the present invention, in each of the discharge circuits of the two hydraulic pumps to which each of the hydraulic actuators for the boom, the arm, and the swing is connected, the on / off switching of the merging / diversion switching valve and the swing load sensing pressure to each of the hydraulic pump circuits. In order to select the required flow rate of each of these hydraulic actuators in accordance with the work content, a work mode including a boom priority, a swing priority, and a standard is selected. Since the adaptation during simultaneous operation of arm rotation can be performed smoothly, the operator must control the spool opening of the flow control valve and control the supply flow rate to each circuit every time the lifting rotation is performed, resulting in fatigue. This eliminates the necessity of the operation that accompanies, and the workability is further improved. Moreover, since the pump is controlled by the load sensing pressure, the energy saving effect is further improved.

[Brief description of the drawings]

FIG. 1 is a hydraulic control circuit diagram showing an embodiment of the present invention, and FIG.
(A) is an explanatory view showing a boom raising and arm dump state of the hydraulic excavator, and (B) is an explanatory view showing a turning state in which excavated earth and sand is loaded to a dump truck stop position. 1 ... Slewing motor, 6 ... Boom cylinder, 7 ... Arm cylinder, 10,13 ... Variable displacement hydraulic pump, 12,15,1
6 ... Flow control valve with pressure compensation, 19 ... Pilot pump, 22a, b, c ... Operation lever, 23 ... Controller, 25a
~ 25 f ...... pilot valve, 27a, 27 b, 27 c ...... pressure compensating valve, 28a, 28 b ...... load sensing regulator, 40 ...
... turning the load sensing pressure switching valve, 44a, 44 b ...... load sensing valve, 47 ...... confluence, shunt switching valve, 50, 52 ...... pilot valve, 54 ...... work mode selector switch.

Claims (2)

(57) [Claims] 1. Two variable displacement hydraulic pumps, and boom, arm, and swing hydraulic actuators driven by hydraulic pressure discharged from each of the variable displacement hydraulic pumps;
The flow control valve with pressure compensation for controlling each hydraulic actuator, and the discharge flow rate of each of the variable displacement hydraulic pumps is determined by the differential pressure between the discharge pressure of each of the variable displacement hydraulic pumps and the maximum load pressure of each of the hydraulic actuators. A hydraulic control circuit of a hydraulic excavator provided with a load sensing system for controlling the hydraulic pressure of the hydraulic pumps (10, 13); A swing load sensing pressure switching valve (40) for turning on and off the load sensing pressure of the swing actuator, and a work mode switch for selecting one of a standard mode, a swing priority mode, and a boom priority mode according to the work content. A switch (54) and a selected signal from the work mode changeover switch (54) are input and stored in advance corresponding to the signal. Based on the stored data, the merging / shunting switching valve (47) is switched to the merging / shunting position and the turning load sensing pressure switching valve (40) is operated.
A hydraulic control circuit for a hydraulic excavator, comprising: a controller (23) for outputting a command signal for switching to an ON position or an OFF position. 2. The work mode selected by the work mode changeover switch (54) is such that the merge / divide switch valve (47) is at the merge position and the swing load sensing change valve (40) is ON.
(Off) position and standard mode, and merge / shunt switching valve (4
A turning priority mode in which 7) is a branching position and the turning load sensing switching valve (40) is in an OFF (on) position, and a merging / shunting switching valve (47) is a branching position and a turning load sensing switching valve. The hydraulic control circuit for a hydraulic excavator according to claim 1, further comprising a boom priority mode in which (40) is set to an ON (off) position.